It is known from the literature that nitrosamines are formed in removal of CO2 from flue gases from power plants fired using fossil fuels. These nitrosamines result from reactions of the NOx gas components present in the flue gas and the amines present in the solvents for the CO2 scrubbing. According to the information available so far, these reactions preferentially take place with secondary amines, which are always present in the industrially synthesized amines. In addition, primary amines combine with the oxygen present in flue gas to form decomposition products which also include secondary amines. It may therefore be considered certain that nitrosamines are formed in the aqueous amine solution and also accumulate there, regardless of whether primary, secondary or tertiary amines are used for the CO2 scrubbing.
Nitrosamines are considered to be carcinogenic substances. It is therefore necessary to ensure that the nitrosamine content of the amine solution is limited to the extent that nitrosamine compounds are not discharged with the flue gas from the CO2 scrubbing. As long as the nitrosamine concentration in the amine solution is low, a secondary scrubbing stage installed in the CO2 absorption column is used to ensure that the nitrosamines are always backwashed and remain in the solution. However, if the nitrosamine concentration continues to increase, there is the risk that nitrosamines might enter the off-gas of the power plant.
It is known that nitrosamines decompose in the atmosphere, which reduces the environmental threat, but it is questionable whether nitrosamines decompose rapidly enough in the atmosphere. In comparison with off-gas consisting essentially of nitrogen, nitrosamines have a significantly higher molecular weight with a high boiling point accordingly and therefore have a tendency to settle to the ground because they are heavier than air. For health and safety reasons and also for environmental protection reasons, it is therefore necessary to ensure that no nitrosamines enter the environment from the solvent circulation. This can be achieved, as mentioned above, if the concentration of nitrosamines in the solvent circulation is limited and an unhindered increase in the amine solution is prevented.